For a structure formed with a magnetic substance such as a large iron structure, attraction to the structure can be performed by magnetic force. Therefore, for the maintenance/inspection of a structure such as this, etc., there has been developed a wall surface attraction type moving apparatus which can make a moving body attract to a structure by taking advantage of magnetic force. In such a wall surface attraction type moving apparatus, since a moving body is caused to be attracted to a structure by magnetic force, the travel of a moving body can also be performed even if the surface of a structure on which the moving body travels is not vertically present downward, i.e., even against a vertical surface.
For instance, FIG. 7 is a schematic constitution diagram showing a conventional wall surface attraction type moving apparatus, and as shown in FIG. 7, the moving apparatus is constituted by a moving body (moving carriage) 110 travelable along the surface of a structure, and travel wheels 112 and 113, a magnetic force type attraction mechanism 130, and a manipulator 120 for operations such as maintenance/inspection, respectively installed in this moving carriage 110.
Particularly, the attraction mechanism 130 is provided with an advancing/retreating rod 132 projected from the lower surface of the moving carriage 110, a permanent magnet (hereinafter referred to as a magnet) 134 installed on the point end of this advancing/retreating rod 132, and a drive mechanism 131 or driving the magnet 134 to leave or approach a magnetic travel surface (magnetic wall surface) 102 under the moving carriage 110 by advancing or retreating the advancing/retreating rod 132.
And in order to adjust the distance between the magnet 134 and the travel surface 102 and adjust the magnetic force (i.e., attraction force) of the magnet 134 by controlling the drive mechanism 131, a force sensor 133 and a controller (attraction force control section) 135 are provided. The force sensor 133 is installed in the proximity of the magnet 134 and detects the strength of magnetic force which acts between the magnet 134 and the travel surface 102. The attraction force control section 135 receives a detection signal corresponding to the magnetic force (i.e., attraction force) between the magnet 134 and the travel surface 102 from this force sensor 133. This detection signal controls the drive mechanism 131 with feedback control based on the detection signal so that this magnetic force (attraction force) becomes a predetermined value, thereby adjusting the advancement/retreat quantity of the advancing/retreating rod 132 and adjusting the distance between the magnet 134 and the travel surface 102.
In other words, the magnetic force (attraction force) acting between the magnet 134 and the travel surface 102 varies in correspondence to the distance between the magnet 134 and the travel surface 102. Therefore, in order for a predetermined magnetic force to act between the magnet 134 and the travel surface 102, the distance between the magnet 134 and the travel surface 102 needs to be controlled in correspondence to this predetermined magnetic force. The attraction force control section 135 controls the distance between the magnet 134 and the travel surface 102 through the drive mechanism 131 so that the magnetic force acting between the magnet 134 and the travel surface 102 becomes a predetermined magnitude, while the detection signal of the force sensor 133 is being fed back.
With such control by the attraction force control section 135, for example even if the travel surface 102 has irregularities thereon and is in a state like an uneven ground, the position of the magnet 134 will be adjusted in correspondence to this travel surface 102 and therefore the attraction force by the magnet 134 can be held nearly constant at all times. In other words, with such control, the gap between the magnet 134 and the travel surface 102 to which this magnet 134 is opposed becomes constant at all times and the required attraction force is stably exhibited, whereby the attraction of the moving carriage 110 to the travel surface 102 is performed with reliability.
Incidentally, in the case where a wall surface attraction type moving apparatus such as the above-mentioned rides across an obstacle on the travel surface 102 such, for example, as a projection 102A shown in FIG. 8 or level difference 102B shown in FIG. 109, there is a need to adjust the advancement/retreat quantity of the advancing/retreating rod 132 so that the magnet 134 is not interfered with by the obstacle.
However, as shown in FIGS. 8 and 9, in the case where the apparatus rides across the projection 102A, level difference 102B, or the like, the magnet 134 must be moved away from the opposite travel surface 102 in correspondence to the height of the projection 102A, level difference 102B, or the like. If done in this manner, the magnet force acting between the magnet 134 and the travel surface 102 will be considerably reduced and therefore it will be difficult to ensure attraction force necessary to cause the moving carriage 110 to be attracted to the travel surface 102 with reliability. Of course, if the magnet 134 is made powerful, attraction force can be increased, but this is undesirable because, in order to ensure necessary attraction force, an extremely large magnet 134 is needed, a considerable increase in the weight or size of the moving apparatus is incurred, an increase in the capacity of a drive unit such as a motor associated with travel drive is required, and so on.